In many areas of industry, it is often necessary to reduce the pressure and energy of fluids (both liquids and gases) within a pipeline. One or more control devices may be employed for this purpose. Various designs for control devices have been presented in the art. For example, a device may be employed to divide the flow through the device into a plurality of separate streams configured as a plurality of tortuous fluid flow paths within the device. As fluid passes through the tortuous fluid flow paths, the fluid is caused to change direction many times. Furthermore, as the fluid travels through the tortuous fluid flow paths, the overall cross-sectional area of the fluid flow path may increase to provide a decrease in the velocity of the fluid within the flow path. The fluid pressure and energy of the fluid is partially dissipated along such paths as a result of losses caused by friction between walls of the path, rapid changes in fluid direction and expansion or contraction chambers. These devices may include what are commonly referred to as “tortuous path trim devices.”
Fluid flow control devices may conventionally take the form of a stack of disks or a plurality of concentric cylindrical sleeves. In the former design, a plurality of substantially planar disks is stacked on top of one another to provide a hollow, cylindrical structure. Such structures are commonly referred to as “valve trim disk assemblies.” Each disk generally includes a plurality of voids formed through the disk. The disks are aligned and stacked together such that a plurality of continuous, tortuous fluid paths are provided by the voids in the disks that extend from the central region of the hollow, cylindrical valve trim disk assembly to the exterior of the valve trim disk assembly. In the latter design, the sleeves are radially perforated with the perforations of adjacent sleeves being offset to cause the fluid to flow in a tortuous path. The sleeves are separated by intermediate annular passages which allow the fluid passing therethrough to expand before it then has to contract to pass through the perforations of the next sleeve. The specific geometric arrangement of such designs is configured to allow the pressure of the fluid of each stream to drop in relatively small increments and in many stages.
A fluid flow control device is often provided within a body of a valve, such as a control valve, having a body that is conventionally configured to direct the fluid from an inlet towards the hollow, cylindrical fluid flow control device. The valve also may be configured to direct fluid passing through the fluid flow control device to the exterior thereof towards a fluid outlet. The valve includes a piston, ball, disk or other device configured to be inserted into a central region of the valve to interrupt fluid flow through and close the valve.
Pressurized fluids contain stored mechanical potential energy. The fluid flow control device dissipates this energy by reducing the pressure and velocity of the fluid. As the fluid flows through the fluid pathways, the fluid flow may be turbulent. Turbulent fluid has associated pressure and velocity fluctuations that act upon the structural elements of the pipes and fluid control devices in which the fluid is flowing. These pressure and velocity fluctuations are generally accompanied by other problems such as erosion, noise, vibration and cavitation. In many applications, these accompanying problems are undesirable or unacceptable characteristics of a fluid flow control device.